#include <stdio.h>
double average(double,double);
int main(void)
{
	double x,y;
	
	scanf("%lf %lf",&x,&y);
	printf("%0.2f",average(x,y));
	
	return 0;
}

double average(x,y)
double x,y;
{
	double average;
	
	x=1/x;
	y=1/y;
	average=(x+y)/2;
	
	return average;
}
